The purpose study is centered around defining in greater detail the neuronal organization of subcortical visual centers, particularly of the upper layers of the superior colliculus, in normal and experimental animals. The object of the work is to answer some questions concerning the structural basis of the centeral processing of visual information, how the neurons and synapses involved develop and how they are modified by injury at different stages of development. Most of the work will use the rat, but where appropriate, monkeys and frogs will also be studied. Experimental material will be examined with light and electron microscopes. It is hoped to derive from these studies some general conclusions regarding the nature and interactions of different factors controlling the development of the highly ordered mature visual system.